Enable directory listing for hosts

The HostControllerInterface does not specify a method to list the contents of a folder. This would be a good helper in lots of scenarios.

The HostControllerInterface specifies the method public function listFolder(string $path, bool $recursive = false, bool $includeFolders = true): array;
$path specifies the folder path
$recursive specifies if the folder sould be searched recursively
$includeFolders specifies if folder names should be included in the output
All existing HostControllers must implement the method